Disc screens are used for screening or classifying discrete materials such as wood chips, municipal wastes, and the like. Disc screens are made up of a screening bed with a series of co-rotating, spaced, parallel shafts, each of which has a longitudinal series of concentric screen discs which interdigitate with the screen discs of the adjacent shafts. Spaces between the discs (Interdisc facial opening, "I.F.O.") permit only material of specified size or smaller to pass downwardly through the bed of rotating discs. Since the discs are all driven to rotate in a common direction from the infeed end of the screen bed to the outfeed or discharge end of the bed, the particles of material which are larger than the specified size of material will be advanced on the bed to the outfeed end of the bed. Disc screens may be used for removing either oversize or undersize material, so that either flow may be accepts or rejects, depending on screen usage.
Prior disc screens employing screen discs rigidly attached to the co-rotating shafts were susceptible to damage from unwanted inclusions in the material to be screened such as large chips, rocks, or other foreign matter. These foreign objects tend to enter the screen and lodge between the discs, becoming trapped. With the discs being held rigid, the result may be the breakage of the discs or the destruction of the proper screening function.
The disc screen of U.S. Pat. No. 4,653,648 utilizes resilient plastic ring-shaped spacers inserted between the screen discs and placed under compression. Disc screens with flexible spacers permit the discs to flex so that minimally oversized chips and other objects which otherwise would wedge between discs will be allowed to pass through the screen. U.S. Pat. No. 4,741,444 discloses a disc screen with resilient plastic spacers and metallic surrounds substantially covering the outside surfaces of the spacers to protect the less-durable plastic from gouging and wear. Additional teachings of resilient spacers can be found in U.S. Pat. Nos. 4,972,959 and 4,972,960 and my co-pending U.S. application entitled "Disc Screen With Controlled Interfacial Openings" filed Mar. 18, 1991.
It would be desirable to fabricate a disc screen with resilient plastic spacers that required fewer parts and that would grip the screen discs on three faces, providing an advantageous snug fit while at the same time ensuring added flexibility and resilience for effectively handling large foreign objects.